Power system control



1951 E. H. FREDRICKSON 2,575,053

POWER SYSTEM CONTROL Filed June 27, 1946 TROLLEY BREAK nfzsm w: RE Tl/RA/(RA IL) INVENTOR.

Ww-M

ATTORNEYS.

Patented Nov. 13, 1951 POWER SYSTEM CONTROL E. Harold Fredrickson, Philadelphia, Pa., assignor to I-T-E Circuit Breaker Company, Philadel phia, Pa., a corporation of Pennsylvania Application June 27, 1946, Serial No. 679,624

4 Claims. 1

My invention relates to electrical systems, and more particularly relates to electrical systems employed in mines for protection against fire hazards.

In the power supply systems to mines, a danger of falling roofs exists which may become a fire hazard if the electrical protective equipment which is at a remote point and which usually consists of a reclosing circuit breaker operates to reclose the line on a short circuit which has been caused by a falling roof.

It is desirable in such systems to provide circuit arrangements which will permit reclosing of the circuit breaker in response to normal faults but will prevent the reclosing of the breaker in the event the fault has been caused by a falling roof.

It has heretofore been proposed to accomplish this result by a pilot wire which extends along and parallel with the trolley and above it so that, in the event of a falling roof, the break in the trolley wire interferes with the electrical circuit operations for eifecting a reclosing of the circuit breaker.

In such systems, however, the load measuring relay lock-out coils are controlled in accordance with the voltage of the load. It is desirable, however, that independently of any fluctuation of load condition, the reclosing operation of the circuit breaker shall be eifective if there has been no break in the roof and shall be prevented from opcrating in the event that the roof has broken.

Accordingly an object of my invention is to provide a novel circuit arrangement for my mine power circuits in which the control of the reclosing circuits for the circuit breaker is dependent solely on the condition of the pilot wire.

A further object of my invention is to provide a novel circuit arrangement in which reclosing of the circuit breaker is also dependent upon the condition of the load.

There are other objects of my invention which, together with the foregoing, will appear in the following description in connection with the figure which is a circuit diagram of one embodiment of the invention.

With the circuit breaker II in closed position, power is fed from the power line 9 over the contacts of the circuit breaker H through the overload relay l2 to the trolley wire 13, load l4, conductor I5, and returned over the negative return rail [6.

It will now be assumed that the circuit breaker H has been tripped open due to some abnormal circuit conditions resulting in the energization of the overload relay [2, but that there has been no break in the roof in any way effecting the pilot wire. When the circuit breaker contacts open, a by-pass circuit around the contact of the circuit breaker is completed through the contacts I! and I8 and including the load measuring resistor I9.

In this circuit the contacts I1 and [8 are manually operable and normally held closed so that the by-pass circuit is immediately eiiective upon the opening of the contacts of the circuit breaker. Shortly after Opening of the circuit breaker a circuit is completed for testing the condition of the pilot wire 20. This circuit extends from conductor 9 through the contacts I! and I l-I, resistor 53 through the winding of the load measuring relay lock-out coil 2|, the pilot wire 20 and thence to the trolley wire 13 and to the load [4.

The contact I l-l in this circuit is mechanically connected to the contacts of the circuit breaker H and so arranged that with the circuit breaker in closed position, contact ll-l is opened. A short interval of time after the circuit breaker contacts have been tripped open, contact I l-| is arranged to close completing the above described circuit and effecting energization of the load measuring relay lock-out coil 2| if the pilot wire is not broken and is connected to the trolley wire [3.

It will be noted that the pilot wire 20 parallels trolley l3 and extends above it. Both are suspended by insulators 22 and 23 from a mine roof 24. The essence of the present invention, as will appear from the description herein, resides in preventing reclosing of the circuit breaker ll if the roof falls causing a break in the pilot wire as schematically illustrated at 25.

The load measuring relay lock-out coil 2| when energized over the circuit described above including the pilot wire 20 functions to remove a latch 26 to permit the operation about to be described.

It will be noted that in parallel with the above described circuit for the winding of relay 2|, a circuit extends over the lower conductor 28 and the second resistor 54 to the conductor 29 and thence to the negative return rail 16. This circuit insures operation of relay 2! irrespective of load conditions, the first described circuit being effective only if there is a load on the circuit. If there is no load on the circuit at the time the circuit breaker operation occurs, then the relay 2! will find an energizing circuit from power supply 9 over the trolley I3, over the pilot wire 20 and through winding 2| in a reverse direction from that described above, and thence over the conductor 28, resistance 54 and conductor 29 to the negative return rail l6. Thus relay 2| will be smote energized whether there is or i not a load at M and irrespective of the condition of the load, the current flow through winding 2! merely being reversed in the case of no load, or over the load circuit when a load does exist at [4.

A further energizing circuit is at this time established from the mid-point of, the load :mease uring resistor l9 thro ugh resistor 3l to load measuring relay holding coil 32. Energization of the winding 32 at this time functions to maintain its armature contacts 33 in disengaged condition".

It will be noted that the relay 34 comprises t'wo. windings 32 and 36. Winding 32 is the load measuring relay holding (5011,"; the circuit for which has just been described. winding iifiiisthe :1 the load measuring load measuring relay closing coi l. An armature 21 pivotally mounted at 33 is normally biased by a spring 39 mounted at 40 and normally holds the armature 21 disengaged from contacts 33; gnaddition to the contact I l-.l which is me 'eauyj erjinhe ted to. the circuit breaker h the arm ,65, the, springjfil'and the time y device 62aiid'is operate thereby, the co'ntaEt'.. t| 2 also mechanically controlled by the breaker and is arranged to close a short 25 interval of time after the closing or contact I I l-l. Cfl dsingof the contact ll-2 extends an energiz ing circuit from the life .9 through contacts IT to" thevmi'd'epei ht 6f tlieIlo'ad measuring resistor {Bland through the closed contacts H--2 and l'..'and resistor 52 th'rough the winding of the lqad iil e asilfiiig relay 'CI'OSih'g coils 36 t0 the Rega tive returnrail l6. I: t"w""l b noted that the energizing current through the winding 36 is dependent on the voltage drop throughohe-half of the windings of the lqaluuhjeasun g resistor .I'Q a'nd on the voltage agre s the load I4. This is because the portion oi the circuit trace above. for the. winding 35 is parallelled by a second cirf'c'uit' through the secnd half er theresistor 'l's thro'ugh contacts to t e trolley (san thence over thefault or'load to r turn wcoriductor I Thejvbl'tage across the w iqihg 36 the eroreiis tha't voltage from the mid: point-9f the resistor 119 through the i right ha f Winding thd thib fi'gl'i the fault. This is in dis;- t iriction from the v energization, of i the windingj32 which'is connected jaeres s theseeohd half or the load rj easiirin'gres'istorflfi.

. r the short eneu t'issever W the voltage time 50 h s h an arm ,wi'iid'iiig 3.6. wi1lfiiotbesuificiently energized to pull armature 12.1 against the n 1; or spring '39, Ii,fhdwever; hormalfcond tiOIis Obtain at the ICiifd, Wilidifig 36 is energized and operates armature 21.jto,engage"contacts133. g Agcireuit is thereupon eo'mpleted from the power flii'ie 9. and contact 11 over conductor 45 through closed contacts lZ-.-l (overcurrent reray. [2. is now derehergized) and contacts 33 didsdbythe energi Za'tiQh Of Windingf36 ('9; scribed above) and through the normally closed cbiitacts ll--3 through (the windin of closing c rol relay 41 to, the negative return ran "it. Relay 4! is thusjenergized in preparation for reeiesm' the, circuit breaker in view of the s which has been made by relay 36 which indicated that the short, circuit was not severe, and in view bptne energization o relay 2| which indicate'd that the failure was notjdue to a break' of the trolley wire. Reclosingoperations of the 'circuitbreaker would now be set in the operation "of t ,tingtheshort The above described cir'cuit included. contact "H which is an -aux) "witch contact, and operated to erased po'siti'oii when the circuit breaker is'opehed;

Energization of the relay 4'! as a result of the above described circuit closes its armature contacts 41-l and completes an energizing circuit for the reclosing winding 48.

Although a circuit for this relay had previously been closed over the resistance 49, this resistance was of such avalue as to prevent energization of the winding 48'. Uponft he clo's'ingof the confacts lT- l a by 'fiass circuit around 49' is provided permitting sufiicient current to flow through "the winding 48 for its energization.

As a result of operation of reclosing magnet 48,

the circuit breaker is reclosed. The first effect of the reclosing ofthe circuit breaker H is to I However, the circuit for relay lock-out coil 2! is still at this time completed over the trolley wire 13 andthrough the pilot wire 20 and over conductor 28176 the negative return rail IS.

The opening of the contacts ll2 which follows the reclosing or the circuit breaker does not at tiirl'e de energ'i'ze the winding 38 since this relay will find an energizing circuit through the closed contacts H-4 which are auxiliary switch contacts closed when the circuit breaker is closed.

This circuit extends from the power line I? over trolley 13 through the pilot wire 20, contacts I l-4- and through the winding to the. negative ree turn rail it; This circuit. was not sufficient to energize the. relayprevi'ously because the. drop in resistors BI and 52 reduced. the current belowthe pull up value for-theuwinding 36, but this current is sufficient to maintain the winding 33,

energized.

' result, however of the reclosing-oi the circuit breaker 1 I, closing control relay 4]. is vde-v energizedby'the openingofcontact's, 1 I 3. M Deenergization of relay 4'! opens contacts 4ii and allows the closing magnet winding 48 to remain energized by a circuitqexteriding'frcm contact 33, through resistor. 49, through winding 48; and to the negative return rail 16.

The circuit breaker is now back in normal op: crating conditionhandif the-fault vis cleared, will remain closed. ,If the fault again occurs, the above. described operations .in general are. repeated following the fenergization. of 'overcurrent relay. [2 'which' trips-the breaker closing contacts Il-l, [If-2, H 3, etc. Reclo'sin'g control relay 4! is re-en'ergized for starting the reclosing operations. v a a has been stated, it is desired that the above described reclosing features shall not be efiected when the pilot wire 'brea'ksan'd the circuit breaker't'rips for this reason, and "itiwi'll now be as-' sumed that-fsuch a condition obtains. In're- 'ponse "to a break-"in the pilot wire; the'energizing'circ'uit "above described for the 'relay "M has opened at the poiiitof "breaksirice it will be re.'-

called the circuit for relay 2| was completed also 6p the circuit for the windingie at the contacts "33" t0 prevent reclosing of the circuit breaker. Accordingly'iion'eof the previously desci'ibe'd operations can be efiected *fdr reclosing egszaoss 5 the breaker and the: breaker willtherefore remain open until the pilot wire has been repaired. When the pilot Wire is repaired, a circuit is completed for the relay 2| which circuit includes contacts l1, and I8, shunting the circult breaker and includes the pilot' wire now repaired, the winding 2|, the wire 28', the resistor-54, and the negative return rail 16. g

Energization of the may 2| causes it to close contact 2l-I and if now the load is normally open-circuited or if, there is no excessive load or short circuit, the winding 36; may be re-energized in the manner described in detail abovefor reclosing thei'circuit breaker.;i; i

Summarizing the above, the sequence of operations is as follows:

1. When the circuit breaker II is in the open position, control current is by-passed around the circuit breaker and through the manual control switches l1 and I8.

2. This by-passes a load measuring current around the circuit breaker ll through the load measuring resistor l9 through the load and back to the negative return.

3. The closing of the advanced time delay closing contact I ll places the load measuring relay lockout coil 2| across the load measuring resistor l9. If the pilot wire is broken due to a roof fall, the load measuring relay lockout coil 2| will not pick up. This leaves the load measuring relay contacts 33 latched Open. If the pilot wire is intact, the lookout coil 2| unlatches the load measuring relay contacts 33.

4. The closing the delayed time delay closing contact ll2 places the load measurin relay holding coils 32 and closing coils 36 in proper relation for measuring the resistance of the load circuit.

5. If the load conditions are satisfactory, the load measuring relay contacts 33 close and energize the closing control relay 4! which picks up and short-circuits the resistor 49 causing the circuit breaker H to close.

6. The closing of the circuit breaker H opens the time delay contacts Il2 and ll-l, opens the auxiliary switch contacts l|--3, and closes the auxiliary switch contact H-4 which energizes the load measuring relay closing coils 36 by means of the pilot wire.

7. If the pilot wire breaks, these coils are deenergized and the load measuring relay contacts 33 open thus opening the circuit breaker I I.

It will now be clear that the systems of the invention herein described reside in the preparatory circuit efiected mechanically by the energization of the relay 2 l.

The winding 38 which is operable over a range of voltage of about 100 volts is not marginal and will effect reclosing of the breaker unless a very serious short circuit condition obtains. In order to accomplish this result, the energization of winding 36 is independent of the pilot wire, its energizing being completed at half the voltage drop of the resistor l9. On the other hand, by my novel arrangement energization of the winding 36 can only be effected when relay 2| is energized over a circuit which is controlled by a pilot wire. This I provide a relay which is independent in its energization of the load or its condition but nevertheless cannot be effective unless the pilot wire is in operative condition.

I claim:

1. In a power protective system, a source of energy, a load, circuit connection therebetween. a circuit breaker connected in said circuit cona. nection for controlling the application of power from said source to the said load, said circuit breaker having reclosing means for reclosing said circuit breaker in response to a fault, a pilot wire extending along and above said circuit and electrically'connected to said circuit at said load, electromagnetic means connected to said pilot wire, a load measuring relay means including circuit-connections whereby said load measuring relay measures the load conditions, means including circuit connections whereby said reclosing means is controlled by said load measuring means, and means controlled by said electromagnetic means in said pilot wire circuit for controlling an effective portion of said load measur- 7 ing relay, said last mentioned means comprising a latch in mechanical relation with the armature of said load measuring relay and preventing its operation when said electromagnetic means connected by said pilot wire is de-energized.

2. In a power protective system having a source of power, a load, circuit connections from said source of power to said load, and a circuit breaker connected in said circuit for controlling the circuit from said source of power to said load, means responsive to predetermined circuit conditions for tripping said circuit breaker, means for reclosing said circuit breaker, a relay having an armature and controlled by said load conditions for controlling said reclosing means, a pilot wire adjacent and connected to said circuit at its terminus, an electromagnetic means connected to said pilot wire, circuit connections including said source of power, pilot wire and electromagnetic means completed to energize said electromagnetic means and operative to de-energize said electromagnetic means when said pilot wire breaks, and a latch mechanism engageable with the armature of said relay and controlled by the energization of said electromagnetic means upon a break in said pilot wire for preventing the operation of said last mentioned relay.

3. In an electrical mine protective system, a circuit extending from a source of power to a load, a circuit breaker connected in the circuit from said source, means responsive to load conditions for opening said circuit breaker, means responsive to the opening of said circuit breaker for reclosing said circuit breaker, means including a pilot wire extending along said circuit responsive to a failure of the mine roof for preventing reclosing of said circuit breaker, and comprising a relay having an armature and controlled by said load conditions for controlling said reclosing means, an electromagnetic means connected to said pilot wire, circuit connections including said source of power, pilot wire and electromagnetic means completed to energize said electromagnetic means and operative to de-energize said electromagnetic means when said pilot wire breaks, and a latch mechanism engageable with the armature of said relay for preventing the operation of said last mentioned relay when the pilot wire breaks, said load controlled relay being responsive to a repair of said roof for automatically restorin said circuit conditions for reclosing said circuit.

4. In a power protective system having a source of power, a load, a circuit from said source of power to said load and a circuit breaker for controlling the circuit from said source of power to said load, means responsive to predetermined circuit conditions for tripping said circuit breaker, means for reclosing said circuit breaker, a relay controlled by said load conditions for controlling 

